How can I calculate what week of pregnancy I am in?

Trying to figure out what week of pregnancy you are in can sometimes be confusing. Adding to the confusion is that there are at least two ways to talk about the weeks of pregnancy. The first way measures pregnancy from the first day of your last menstrual period. The second way to calculate which week of pregnancy you are in will measure from the time that you were ovulating.

In the United States, it is most common to calculate what week of pregnancy you are in by looking at the date of your last menstrual period (LMP). From the start of your last menstrual period until the time you give birth it is, on an average 280 days. This comes out to exactly 40 weeks. The trimesters of pregnancy are spaced out somewhat evenly during the weeks, with about thirteen to fourteen weeks for each trimester.

If you know when your last menstrual period started, you can know what week of pregnancy you are in. If you don’t know when your last menstrual period started but you do know when your baby was conceived, you can simply count backwards roughly two weeks to know when the start of your pregnancy was.

If you’re not sure about either when your last menstrual period started or when you conceived, there are a few ways to calculate what week of pregnancy you are in. Your health care provider will generally do a series of measurements as you go through pregnancy, to know how your baby is growing. Sometimes, a health care provider may be able to help you determine what week of pregnancy you are in using these measurements. Another method of knowing what week of pregnancy you are in would be with an ultrasound. Because the ultrasound also takes specific measurements of your baby, the growth rate can also here help your health care provider to know what week of pregnancy you are in.

If you don’t know what week of pregnancy you are in and are having a hard time figuring it out, you should speak with your health care provider. She may be able to help you determine how far along you are.